This invention relates to a composite-structure comprising a substantially monocrystalline growth substrate with at least one monocrystalline or polycrystalline layer of diamond or diamond-like material arranged thereon and to a process for producing such a composite structure.
U.S. Pat. No. 5,082,359 discloses a process for producing a polycrystalline diamond layer on, for example, a silicon substrate. Prior to the deposition of the diamond layer, for example, by means of a hot wire CVD (Chemical Vapor Deposition) process described in JP 62-278,196, the free surface of the silicon substrate is pretreated to intentionally generate irregularities on the free surface. These irregularities, which destroy the smooth structure of the free surface (for example: craters, fissures or cracks, etc.), can be introduced into the free surface by means of chemical etching or plasma etching, by means of at ion beam, by means of a laser, etc. Powdered diamond crystals from an external source are subsequently embedded in these disturbances or irregularities, in particular by being rubbed in. The embedded diamond crystals then can serve as growth crystals for the diamond layer which is deposited after the embedding of the individual powdered diamond crystals. This nucleation of the free surface, however, is both very labor-intensive and cost-intensive. Furthermore, the deposited polycrystalline diamond layer of the composite structure only exhibits a small degree of orientation relative to the crystal lattice of the growth substrate. As a result of this limited orientation, the diamond layer is only suitable to a limited extent for subsequent application of electronic components and/or for epitaxial growth of a further layer, in particular a semiconductor layer, since this low orientation of the diamond layer adversely affects the function of the components and/or the quality of the further crystal layer.
The object of the invention is to further develop the basic composite structure to such an extent that it is better suited for application of electronic components.
Another object of the invention is to improve the basic composite structure so that it is better suited for epitaxial deposition of subsequent crystalline layers, in particular semiconductor layers.
A further object of the invention is to provide a process for producing a composite structure of the foregoing type with which such composite structures can be produced as simply and inexpensively as possible.
These and other objects have been achieved in accordance with the present invention by providing a composite structure comprising a substantially monocrystalline growth substrate having a crystal lattice, and at least one monocrystalline or polycrystalline layer of diamond or diamond-like material deposited on a surface of the growth substrate, in which the surface of said growth substrate is provided with crystal growth nuclei, at least 50% of the growth nuclei having crystal axes exhibiting not more than 10% inclination relative to corresponding axes of the growth substrate crystal lattice.
In accordance with a further aspect of the invention, the objects have also been achieved by providing a process for producing a composite structure comprising a growth substrate and at least one monocrystalline or polycrystalline layer of diamond or diamond-like material arranged on a surface of the growth substrate, which process comprises depositing crystal growth nuclei on the surface of the growth substrate by chemical vapor deposition from a nucleating gas phase comprising a diamond precursor, the growth substrate having a negative electrical potential applied thereto relative to the nucleating gas phase, and then depositing said layer of diamond or diamond-like material on the surface provided with growth nuclei by means of hot wire chemical vapor deposition from a depositing gas phase.
By means of the xe2x80x9cin-situxe2x80x9d nucleation of growth nuclei on the growth substrate in accordance with the invention, the subsequent deposition of the diamond layer thereon is effected with a good orientation of the diamond layer.